The general procedure of drilling an oil or gas well includes drilling a borehole using a drilling fluid. The use of an organic based drilling fluid or drilling mud such as an oil based drilling fluid (also known as oil based mud) or a synthetic based drilling fluid (also known as synthetic based mud), has become increasingly popular since their introduction in the 1950's. Oil based muds and synthetic based muds offer advantages over water based muds in many drilling situations. In particular, oil based muds are known in the art to provide excellent clay stabilization and shale inhibition, borehole stability, lubricity, thermal stability, corrosion inhibition, tolerance of contamination, and ease of maintenance.
Subsequent to drilling the borehole, casing is run into the well and a cement slurry is then placed in the annulus between the outside of the casing and the borehole wall. In order to obtain a good cementing job, it is necessary for the cement slurry to displace substantially all of the drilling mud from the annulus. Once placed, the purpose of the cement slurry is to harden in the annulus and provide an effective seal between the casing and the borehole. The hardened cement sheath prevents or inhibits communication of fluids between the various formations penetrated by the well. In addition to providing zonal isolation, the cement is in contact with the casing and provides mechanical support and resistance to axial movement through the shear bond developed between the interfaces of cement and pipe and cement and formation. However, bonding between the cement and casing and borehole surfaces is not always readily achievable, especially where the drilling fluid and cement are not compatible, which is not uncommon. In particular, the oil wetting nature of organic based drilling muds causes incompatibilities with traditional Portland cements in downhole environments. This incompatibility can lead to loss of cement sheath integrity as well as ingress of formation fluids, which then compromises zonal isolation.
During the drilling process, the drilling fluid must stay in the borehole to perform its function(s). Frequently, undesirable formation conditions are encountered in which substantial amounts or, in some cases, practically all of the drilling fluid may be lost to the formation, also known as lost circulation, which can interfere with drilling progress. Drilling fluid can leave the borehole through large or small fissures or fractures in the formation or through pores in the rock matrix surrounding the borehole. The response to such fluid losses is to pump lost circulation materials to stop and remediate the losses. However, due to incompatibilities with organic based drilling fluids, poor bonding to the surfaces of the fracture, or hardening of the cement with too high a compressive strength that will deflect the drillbit when the loss zone is re-drilled, cements known in the art often does not provide a solution for this purpose.
U.S. Pat. No. 5,058,679 describes solidification of water based drilling muds using blast furnace slag. However, a similar process was not successful with organic based drilling muds. With the nearly exclusive use of organic based drilling muds particularly in offshore operations, a different method of mud solidification is needed. The compositions and methods described herein address these and other needs.